Automatic telephone system



Aug. 24, 1937. M. E. GRIFFINS. 9

AUTOMATIC TELEPHONE SYSTEM Filed July 12, 1935 kn o INVENTOR. MORRIS E. GRIFFINS ATTORNEY;

Patented Aug. 24, 1937 UNHTE S'E'A'i' ere tries AUTOMATIC TELEPHONE SYSTEM of Delaware Application July 12, 1935, Serial No. 30,957

13 Claims.

The present invention relates in general to automatic telephone systems, and more in particular to the equipment which is provided to enable the wire chief to test the lines in such systems.

This equipment may comprise a test circuit which includes the instruments. and keys required to perform the tests, one or more test distributors, and a connector for each group of lines. The test circuit is connected to any desired line by operating a test distributor to select the group in which the line is located and by then operating the test connector in that group to select theparticular line to be tested. If there are more than one-hundred groups of lines, test connector selectors may be inserted between the test distributors and the test connectors. The U. S. patent to Crocker, No. 1,576,723, shows a complete testing system of this character.

The system disclosed in the Crocker patent is intended for use in a single exchange and as a practical matter is limited to use in a single exchange, not only because of the number. of conductors required between the test distributors and test connectors (six conductors), but also because the resistance of certain of these conductors would be too high to enable the system to operate properly if it were attempted to give the test distributors in one office or exchange direct access to test connectors in a distant ofiice.

3O Situations frequently arise, however, where centralized testing is desired, that is, it is desired to have the wire chief in one oifice test lines in an outlying ofiice as well as in his own ofiice. The usual method of handling this situation is to provide the wire chief with a direct test trunk extending to the outlying office and terminating therein in a test distributor having access to test connectors. This amounts to a duplication of the Crocker system, separate test trunks and test switches being provided for each office.

While the foregoing arrangement works all right it is objectionable in many situations because it requires the wire chief to select a test trunk in accordance with the office in which the line to be tested is located, and because he is re quired to omit the office designation in dialling the number of the line, which leads to confusion. This latter objection is particularly important where the test switch train is used by the toll operators for verification purposes, it being desirable that the toll operators should dial the directory numbers and not have to omit any digits. There are other objections which need not be gone into, and a demand has arisen, therefore, for a test train which can be used by the wire chief or toll operator to gain access to subscribers lines either in the main oilice or in an outlying office by dialling the regular telephone numbers of such lines.

As an example of where such an improved test train may be used, a telephone system may be considered which comprises several different offices interconnected by trunk lines and forming a network giving service to a fair sized city. If there are less than ten ofiices a five digit num- 10 bering system may be employed, the first digit of any number serving to designate the office while the other four digits identify the line in the office. There are numerous telephone system of this type installed in the United States and other countries 15 and the system is therefore well known.

According to the present invention one of the offices in the system is selected as a testing ofiice and there the wire chiefs desk is located. The toll board may be at the same point if the test 20 train is to be used for verification. .From the wire chiefs test desk four conductor test trunks extend to test distributors. These test distributors, when used to connect with a line in the testing office, respond to two digits and have access to test con- 25 nector selectors. These latter respond to one digit and have access to test connectors, which respond to two digits and make the final line selection; Thus the complete switch train used to connect with a line in the testing office comprises a test 30 distributor, a test connector selector, and a test connector, requiring five digits for their operation. Such a test switch train is shown .complete in the Crocker patent hereinbefore referred ,to. The present invention contemplates using test 3 connector selectors and test connectors of the type shown in the Crocker patent. The test distributor, however, is different from the test distributor there shown.

Now, in order to enable the wire chief to con- 40 meet with the lines in other ofiices the test distributor is also given access to test trunk lines extending to such other offices. Suppose there are three ofiices, for instance, the testing oilice and two other offices. The testing ofilce may 45 have numbers beginning with the digit two, while the other offices may have numbers beginning with the digits three and four, respectively. Then in the second level of the test distributors access is had to local test connector selectors, the 50' These test distributors may be of the type shown in the Crocker patent, or of the type shown in the instant case, and have access to test connectors of the type shown in the Crocker patent. In the fourth level of the test distributors in the testing ofiice, the No. 2 office, access is had to four conductor test trunks leading to test distributors in the No. 4 office. The arrangement in the No. 4 office is the same as in the No. 3 office, comprising test distributors and test connectors.

connections to lines in the No. 2 office.

It will be understood now that the test distributors in the testing office must function differently in setting up connections to lines in the No. 3 or No. 4 ofiice than they do in setting up In the case of a connection completed within the No. 2 office, the test distributor used responds to two digits and selects a particular test connector selector. In the case of a connection to a line in one of the other offices, however, the test distributor used responds only to one digit, the office selecting digit, and is then given an automatic hunting movement to select an idle interofiice test trunk. One feature of the invention,

therefore, is a combined one and two digit test ing lines the wire chief must be able to drop the bridge cut-off relay of a line undergoing test so as to be able to make an inward test of the line, that is, a test toward the switchboard. The bridge cut-off relay is dropped or deenergizes by imposing a certain control condition on the two operating conductors of the test trunk. Another requirement is that the wire chief be able to release the test connector in use without releasing the test distributor. The release of the test connector is brought about by imposing a different control condition on the two operating conductors. A further feature of the invention, therefore, is a test distributor which includes means for relaying or repeating certain control conditions, commonly referred to as B. C. O. and connector release, over an inter-office test trunk to a test distributor in a distant ofiice.

The foregoing and other features will be described hereinafter with reference to the accom panying drawing, which shows diagrammatically sufiicient of the equipment and circuits involved to enable the invention to be understood.

Referring to the drawing, the rectangle TC at the left of the drawing indicates a wire chief s test circuit, which may be the same as the one disclosed in the Crocker patent previously mentioned. The drawing shows only so much of the test circuit equipment as is involved in the description of the instant invention. This cornprises a calling device CD, and two keys labelled Conn. Release and B. C. O. for placing the control conditions hereinbefore referred to on the operating conductors of the test trunk.

Outgoing from the wire chiefs desk there is a four conductor test trunk comprising operating conductors 3 and i and test conductors 5 and 6. The test circuit may be connected to the test trunk by any well known means (not shown), such as a key, or plug and jack.

The test trunk extends to a test distributor,

indicated by the reference character TD. This test distributor is a Strowger vertical and rotary switch of well known mechanical construction. The circuit is novel and will be fully described hereinafter.

The test distributor TD has six wipers 23-28. On the second level these wipers have access to six conductor trunks extending to test connector selectors, as previously explained. One such trunk, comprising conductors 8ll85, is indicated in the drawing. This trunk extends to a test connector selector, and the latter has access to test connectors. Since these switches may be the same as those disclosed in the Crocker patent they are not shown herein.

On the third level the test distributor I'D has access to four conductor test trunks extending to the No. 3 ofiice. One of these trunks is indicated in the drawing and comprises conductors 86--89. This trunk extends to the No. 3 office and there terminates in a test distributor which may be the same as the distributor TD or which may be the same as the test distributor shown in the Crocker patent. In any event, the test distributors in the No. 3 ofiice have access to test connectors of the same type as those previously referred to, i. e., like those in the Crocker patent. Under the circumstances it has not been considered necessary to show the test distributor and test connector used in the No. 3 office.

It will be assumed that the wire chief desires to connect his test circuit with a local subscribers line in the No. 2 office for the purpose of testing such line. In order to accomplish this, the wire chief connects the test circuit to an idle test distributor by means of a key or plug and jack arrangement, as previously mentioned, and then operates his calling device in accordance with the digits in the subscribers telephone number. It may be assumed that this telephone number is 21456.

Assuming that the test circuit TC and the test distributor TD are used for setting up: the con nection, when the test circuit is connected to the test distributor the line relays 8 and iii of the test distributor will pull up over the two operating conductors 3 and 4 in series, these conductors being bridged by the calling device CD in the test circuit. Upon energizing, relay 8 closes a circuit via 3! and 49 for the slow acting release relay ll. Relay 50 also closes a circuit for relay H at 35. Upon energizing, relay H prepares the impuising circuit for the vertical magnet 28 at 38. Relay H also opens the circuit of release magnet 22 at 31.

The wire chief may now dial the first digit of the number, which is the digit 2. Two interruptions are therefore produced in the bridge across the operating conductors 3 and 4, resulting in momentary deenergizations of the line relays 3 and Ill. The operation of relay 8 is without effect at this time, but each time relay ll] falls back it sends an impulse to the vertical magnet 20, the circuit extending by way of 35, 38, oil normal springs VON, winding of the slow acting series relay I2, and winding of the vertical magnet 20 to battery. This circuit is altered at the vertical off normal springs in the well known manner at the first upward movement of the switch shaft, but is maintained by the operation of relay l2 until the impulses cease. Two impulses are therefore delivered to the vertical magnet 20, which step the wipers 2328 up two steps until they stand opposite the second level in their respective banks. The series relay i2 falls back at the end of the impulses for the first digit, and transfers the impulsing circuit to the rotary magnet 2|.

The wire chief may now dial the second digit of the number, which is the digit 1. Accordingly, a single interruption is produced in the control circuit and the line relay I!) sends one impulse to the rotary magnet 2!, the circuit extending from ground by way of 35, 38, off normal springs VON, is, All, E5, and winding of rotary magnet Zi, to battery. The rotary magnet responds to the received impulses and rotates the wipers 2328 one step, bringing them into engagement with the set of contacts in which is ter- 23, minated the trunk comp-rising conductors 8il85.

This trunk line, as previously explained, extends to a test connector selector in the local or No. 2 oflice.

The slow acting relay IB is connected to the impulse circuit in parallel with the rotary magnet EI, and therefore this relay responds to the impulse also. Upon energizing, relay l6 closes a circuit for the slow acting relay ll, the circuit extending from ground by way of 39, 54, 58, and

T winding of relay H, to battery. Upon energizing, relay l'l prepares a test circuit at 6! and prepares a circuit for relay H3 at 62. Shortly after the rotary movement has been completed, the slow acting relay it will fall back and break the initial energizing circuit of relay 1?. At the same time, however, the test circuit is completed over a path which extends from test wiper 26 by way of 5 5, El, lower Winding of test relay i5, and winding of relay ii, to battery. If the test connector selector which has been selected by the test distributor is busy there will be a ground potential on the conductor 8!, and accordingly the circuit just described will be completed, resulting in the operation of relay l5 and the holding up of slow acting relay l'l. Upon energizing, relay l5 opens the impulsing circuit at 55, opens the circuit of relay 8 at 54 to prevent this relay from pulling up, connects a source of busy signalling current to the operating conductor i at 55, and at 53 closes a circuit for the reversing relay 7. The latter relay, upon energizing, reverses the operating conductors 3 and i as regards their connections to the line: relays ii and IE3, thereby reversing the direction of current flow over the operating conductors at the test circuit. These operations result in giving the wire chief visual and audible busy signals, as is well known, and as is fully explained in the Crocker patent hereinbefore referred to.

Assuming now that the test connector selector which has been seized is idle, there will be no ground potential on conductor 8! and consequently when relay it falls back the test circuit will not be completed and relay l5 will not be energized. At the same time that relay 1% closes the test circuit, it also closes a circuit for relay it which extends from ground by way of 39, 53, 53, 52, and winding of relay 18, to battery. This circuit includes the contact 62 of relay H, which is maintained closed for an instant due to the fact that relay l! is slow acting. Upon energizing, relay l8 locks itself at 3 5, opens the rotary magnet circuit at 55, and shifts the test wiper M to the upper winding of relay H5 at 8:3. Relay Iii also closes a bridge across the Wipers and at '31, this bridge including the contact 36 on the line relay l0, which is now energized. Wipers 25 and 26 are now resting on the bank contacts to which operating conductors 82 and 83 are connected, and the bridging of these Wipers therefore closes the operating circuit over conductors 82 and 83 to the test connector selector. The line and release relays of the test connector selector accordingly pull up and prepare the switch for operation.

The wire chief may now dial the next digit 3 of the desired number. Three interruptions are accordingly produced inthe circuit of line relay ifi,=-which falls back three times and produces three interruptions of the bridge of Wipers 25 and 25 at 33. Thesethree interruptions cause deenergizations of the line relay of the test connector selector, and this switch is operated therefore in accordance with the digit 3 in order to select a test connector in the group in which the called subscribers line is located.

While the third digit 3 is being repeated by the line relay I!) to the line relay of the test connector selector, the line relay it] also sends impulses to the slow acting relay i6. Relay it accordingly responds and operates relay ll. Relays EB and I? are accordingly maintained energized during the dialling of the third digit and the latter relay holds the test conductors 5 and 6 open at 68 and 69.

If the operation of the test connector selector responsive to the third digit should result in the seizure of a busy test connector, the test connector selector will place a, battery potential upon conductor 8|, thereby closing a circuit for the test relay E5 of the test distributor TD. This operates relay i5 in order to give the wire chief a visual and audible signal in the manner hereinbefore explained.

Assuming, however, that the test conductor to which the connection has been extended is idle,

no busy signal will be received and the wire chief will dial the fourth digit of the number, which is the digit 4, and also the fifth digit of the numb-er, which is the digit 57 These two digits are repeated by the line relay ii! in the same manner as has been described, and are effective to operate the test connector in its vertical and rotary movements in order to connect with the subscribers line. The conditions at this stage are that the test conductors 5 and 6 are extended by way of conductors 84 and 85 of the trunk to the test connector selector, and thence to the wipers of the test connector which are in connection with the subscribers line. Also the wiper 23 of the test distributor is extended over conductor til and the test connector selector to the test wiper of the test connector which is now in engagementwith the test contact of the called line. During the repeating of the last two digits the slowacting relays l6 and I! of the test distributor respond as previously explained. Upon the falling back of relay iii at the end of the last digit a test circuit'is completed for testing the called line to determine if it is busy or idle. This circuit extends from the test contact of the called line through the test wiper, of the test connector and over the path just describedincluding conductor 8G, to wiper 23 of the test distributor, whence the circuit extends :by way of E33, 43, 6!], 57, and the winding-of the reversing relay I to battery. It the called subscribers line is busy there will be a ground potential on the test contact and the circuit will be closed, resulting in the energization of relay l. Relay I prepares a locking circuit for itself at St) which is completed upon the falling back of relay i'l, relay l being maintained over a path which includes wiper 23, 63, t3, contacts of relay ll controlled by iii 44, 38,

and winding of relay 1. Relay 7 is therefore held up as long as the called line continues its busy condition.

If the subscribers line is idle when called, the relay '1 will not be energized. With relay 7 deenergized, either due to having found the subscribers line idle, or due to the subscribers line having become idle after it was connected with, a circuit is completed over which ground is extended to the test wiper of the test connector, this circuit extending from ground by way of 32, Si), 54, contacts of relay l? controlled by 69, 43, 53, wiper 23, and conductor 80, whence the circuit continues through the test connector selector to the test wiper of the test connector, as previously described. By means of this circuit ground placed on the test contact of the called line, resulting in the energization of the bridge cut-off relay for the purpose of disconnecting the line relay. This clears the line of its normal battery and ground connections so that the wire chief may now go ahead and perform the tests.

As mentioned hereinbefore, one of the tests which the wire chief may desire to perform is the inward test, which requires the dropping back of the bridge cut-off relay of the subscribers line. In order to deenergize the bridge cut-off relay, the wire chief will operate the B. C. 0. key in his test circuit. By the operation of this key the bridge across the operating conductors 3 and A is broken and ground is placed on conductor 3. This maintains line relay i ii energized and permits the line relay 8 to fall back. Relay iii keeps the release relay ll operated so that the distributor is not released, and relay 8 on falling back opens at 32 the circuit over which ground is supplied for holding the bridge cut-off relay of the subscribers line. The bridge cut-off relay accordingly falls back and the wire chief can proceed to make the desired test. After the test is finished the B. C. 0. key may be restored and the bridge cutoff relay will pull up again.

If the wire chief desires to release the switches beyond the test distributor TD while maintaining the distributor operated, he will actuate the connector release key labeled Conn. Release. This key breaks the loop and puts battery on conductor 4, resulting in the holding up of relay 8 and the falling back of relay is. Relay 8 holds the release I I energized, thereby preventing the release of the test distributor. On falling back, relay it breaks the bridge across the outgoing operating circuit at 36, which brings about the release of the test connector and the test connector selector. The wire chief may then restore the connector release key and by further operation of the calling device he can reoperate the test connector selector and the test connector to set up a connection to another subscribers line.

The test circuit TC is usually provided with a release key which will open the loop including the operating conductors 3 and 4 so as to release the entire connection without disconnecting the test circuit from the test distributor. When the release key is operated, or when the test circuit is disconnected from the test distributor, the line relays 8 and Ill fall back, breaking the circuit of the release relay l l. The falling back of the line relay l B will break the outgoing operating circuit and release any switches that may have been set up beyond the test distributor. The falling back of the release relay I l closes a circuit for release magnet 22, which restores the test distributor TD to normal in the usual manner.

It will be assumed now that the wire chief desires to set up a connection to a subscribers line in the No. 3 office. Assuming further that the test circuit TC is connected to the test distributor TD for this purpose, the line relays 8 and it are energized as previously explained, followed by the energization of release relay l l. The wire chief may now dial the number of the subscribers line, which will be assumed to be 34,567.

When the first digit 3 is dialled, the line relay 5 9 falls back three times and sends three impulses to the vertical magnet 26. The vertical magnet responds to these impulses and steps up the wipers 2328 to the third level in their respective banks. The slow acting relay 12, in series with the vertical magnet 29, responds to these impulses also and holds up throughout the series of impulses, maintaining the vertical magnet circuit after the shifting of the vertical off normal springs VON. Relay i2 also closes a circuit at 61 for relay 59, which energizes. When the switch shaft reaches the third level, the shaft springs S are closed, whereupon a locking circuit is completed for relay 59, which extends from ground by way of 38, the right-hand pair of shaft springs S, '55, the interrupter contact of the rotary magnet 2i, and winding of relay l9 to battery. It may be remarked that relay is is energized under control of relay I? when the test distributor TD is used for setting up a connection local to the No. 2 ofilce, the same as it is in the present case, but since the shaft springs S are not closed on the second level, the relay 19 cannot lock itself and its temporary operation by relay i2 is without effect.

Shortly after the impulses for the first digit cease, the slow acting relay l2 will fall back, relay it remaining locked up. On deenergizing, relay l'Z closes a circuit for relay i6 which extends from ground by way of 39, ll, the resistance it, it, and winding of relay It, to battery. Resistance i6 is high enough so that the rotary magnet 22, in parallel with relay i5, is not operatively energized. Relay i ii energizes, however, and at 58 closes a circuit for relay 5%, the circuit extending from ground by way of 39, ll, left-hand pair of shaft springs S, 59, and winding of relay l3, to battery. On energizing, relay i3 locks itself over a circuit extending from ground by way of 39, (ii, resistance it, 48, and winding of relay It to battery. Belay i3 is the change-over relay,

which changes the test distributor TD from a twodigit switch to a one-digit switch and initiates its automatic hunting movement. A large number of circuit changes are brought about by the energization of relay i3 which can be more conveniently brought out in the discussion of the ensuing operation.

With relays l3 and i6 energized as described in the foregoing, a circuit is completed for the rotary magnet 2! which extends from ground by way of 39, ll, left-hand pair of shaft springs S, 59, 38, M, 65, and the winding of rotary magnet 2! to battery. The rotary magnet is energized over the above circuit and rotates the shaft one step, bringing the wipers 2228 into engagement with the first set of contacts in the third level. On energizing, the rotary magnet 25 also breaks the locking circuit of relay iii, which thereupon falls back and breaks the rotary magnet circuit at i i. The rotary magnet accordingly deenergizes and closes its interrupter contacts. When relay l5 energized it operated relay ii in the usual manner, so that at this juncture relays it) and i? will both be in energized condition. The breaking of the rotary magnet circuit at it also breaks the circuit of relay IE, but this relay is slow acting and holds on for an instant. When the rotary magnet deenergizes and closes its interrupter contact, therefore, a new circuit is completed for relay l9, provided the trunk line terminating in the set of bank contacts engaged by the distributor wipers is busy. If this trunk line is busy there will be ground potential on test contact H, and since contacts TH and it are strapped together the ground potential will be picked up by wiper 23 which is now in engagement with con- 1 tact T0. The circuit for energizing relay IQ'therefore extends by way of H, H3, 23, 63, 42 (relay i3 being energized), 69, 51, (relays I? and It being energized), 45, rotary magnet interrupter contacts, and winding of relay is to battery. Relay l9 therefore again energizes and locks itself at 15, reclosing the rotary magnet circuit and the circuit of relay IS at E4. Relays l6 and H are 0 accordingly held energized and the rotary magnet is reoperated and advances the switch wipers another step. The operation of the rotary magnet again unlocks relay l9 and the same testing operation is performed again, relay l9 and the rotary magnet 2i operating alternately as long as the wipers of the distributor continue to find busy trunk lines.

It will be well to stop here for a moment and explain the wiring of the test contacts such as 70 and H which are associated with the group of trunk lines in the No. 3 oifice. These test contacts are connected together in pairs, except for the pair which is associated with the last trunk of the group. For instance, if there are four I trunks in the group of test trunks extending to rotary connectors.

Assuming now that all of the trunk lines are busy, the fourth operation of the rotary magnet 21 will set the distributor wipers 23-28 on the fourth set of bank contacts and will bring about the deenergization of relay H). The fourth trunk line being busy, according to the assumption,there will be a ground on the fourth test contact corresponding to test contact H, but since this test contact is not strapped to the paired test contact corresponding to the contact Ill there will be no circuit closed for reoperating relay l9. rotary magnet accordingly is not reoperated and shortly the slow acting relay It will fall back. The falling back of relay l6 closes a circuit for the test relay IS in series with the slow acting relay ll, the circuit extending from the grounded test contact engaged by wiper 24, by way of said wiper 2'3, 64, El, winding of relay l5, contacts controlled by 58, and winding of relay H, to battery. Relay I 5 accordingly energizes and-relay H is maintained energized. Thus the busy signal is transmitted to the wire chief in the manner previously explained.

Assuming now that an idle trunk line is found, which may be the trunk line 8689,'shown in the drawing, when the rotary magnet 2| falls back after bringing the wipers into engagement with the set of bank contacts in which this trunk line terminates, it closes the circuit of relay I9 as previously explained, but "this relay does not en- The.

The Y ergize because although the test contacts ill-H are strapped together there is no ground potential on test contact H. The rotary magnet circuit is not again closed, therefore, and the slowacting relay it falls back. On deenergizing, relay it closes a test circuit which includes relay is, as previously explained, and also closes a circuit for relay 18, the slow acting relay El remaining momentarily in operated condition. Since there is no ground on the test contact l l, the test relay it will not energize, contact 56. remains closed, and relay I8 is permitted to energize. This relay locks itself at 56. In energized position, relay it connects ground to the test wiper the circuit extending from ground by way of and 53 to the wiper it. This operation places ground on test contact ii and marks the trunk ine busy to other test distributors. Relay l8 also closes the outgoing operating circuit at 61.

The connection has now been extended to the No. 3 oflice. The trunk line 8$59 terminates in that office in a test distributor, which may be the same as test distributor TD. Assuming that such is the case, when the bridge is closed across the wipers 25 and 26, by operation of relay It, the operating circuit over conductors 36 and 81 is completed, and the line relays such as 8 and IU of the test distributor will pull up, preparing it for operation in the manner described in connection with test distributor TD. It will be understood also that the test leads 5 and 6 now extend by way of wipers 27 and 28 and outgoing test conductors 88 and 8% to a pair of incoming test conductors associated with the test distributor in the No. 3 ofiice, these test conductors corresponding to the test conductors 5 and 6 of the test distributor TD.

The wire chief may now proceed to dial the remaining digits of the subscribers number, which are repeated over'the outgoing operating circuit.

comprising conductors 86 and Si by the line relay IE3 at contact 35. The second and third digits are effective to control the operation of the test distributor in, the distant No. 3 office, which accordingly extends the connection to a test connector in the desired group. The fourth and fifth digits are effective to control the operation of the test connector to complete the connection to the subscribers line. Y

It will be observed that since the change-over relay 5% is in energized condition while the digits are being repeated to the distant office, the local impulse circuit in the test distributor TD is broken at 41, so that relays l6 and I1 do not respond.

It will be observed also that since the changeover relay I3 is in energized position, the control circuit extending to the distant office includes the lower winding of the electro-polarized relay M,

the shunt being removed from the lower winding.

of this relay at Ell. .Relay I4 is an electro-polarized relay of the usual type having an upper polarizing winding which is maintained energized at 39 and having a low' resistance winding included in one side of the control circuit. When i the current flow in the control circuit is in the 'normal direction, as it is during the setting up flow over the operating conductors 86-and 87 will If a busy condition should be encountered be reversed. This reversal of current in the control circuit causes the electro-polarized relay [4 at the distributor TD to operate. Relay TD connects a condenser between the operating conductor i and the outgoing operating conductor 87, so that the busy tone can get back, and also closes a circuit for the reversing relay '5 at 5|. Thus the busy signals are relayed back from the test distributor in the distant oflice through the test distributor TD to the test circuit TC.

It should be explained also at this time that with the relay 13 in energized condition the short circuit which normally exists around the lower winding of relay 9 is broken and one terminal of this winding is connected to battery through a resistance 3?. This change in the circuit of relay 9 has for its object the preparing of this relay for operation by the deenergization of either relay 8 or relay i ii, as will be explained hereinafter. In the meantime it may be pointed out that when both these relays fall back together, as during the transmission of impulses, relay 9 does not operate. In order to take care of the contingency that the relays 8 and it may not deenergize exactly tc-- gether relay 9 is provided with a normally short circuited upper winding which makes it very slightly slow to operate.

The connection to the subscribers line in the distant oflice having been established, it will be assumed that the wire chief proceeds to make some tests. If the wire chief desires to drop back the bridge cut-off relay of the called line, he will operate the B. C. 0. key in the test circuit TC. The actuation of this key opens the bridge across the operating conductors 3 and 5 and grounds the conductor 3, which allows relay 8 to fall back and holds up relay ill. Relay it, of course, main-- tains the release relay H energized. As soon as relay 8 falls back relay 9 operates over a circuit which extends from ground by way of 35, lower winding of relay 9, 4E, and resistance H to battery. On energizing, relay 9 breaks the bridge across the outgoing control circuit including conductors 86 and 8? at 33 and also, relay 8 being back, connects ground to conductor 85, the circuit extending from ground by way of 3!, 33, 3t, 67, and through wiper 25 and contact engaged thereby to conductor 89. Thus it will be seen that the same condition that is imposed on the control circuit incoming to the test distributor TD is imposed on the outgoing control circuit comprising conductors 86 and 87 extending to the test distributor in the distant office. At the distant ofiice the test distributor of course responds to this control condition in the same way that was described in connection with the test distributor TD in the establishment of a local connection, and the result is that ground is removed from the circuit of the bridge cut-off relay of the subscriber's line and this relay is allowed to deenergize. The circuit changes described endure only as long as the B. C. 0. key remains actuated, and when this key is restored the circuits resume their normal condition.

Assuming now that the wire chief desires to release the test connector in the distant No. 3 ofiice, he will operate the connector release key in the test circuit TC. By the operation of this key the bridge across the operating conductors 3 and 4 is broken and battery is placed on conductor 4. The result is that relay 8 is held up while relay ii! is allowed to fall back. As soon as relay l falls back relay 9 is energized over a circuit which extends from ground at 3| by way of the lower winding of relay 9 and through the winding of the release relay II to battery. Thus relay 9 is energized and at the same time the release relay I I is maintained operated. With relay l9 deenergized and relay 9 energized it will be seen that the bridge across the outgoing control circuit is broken at 35, while at the same time battery is placed on the lower side of the control circuit at 34. Thus the condition imposed on the conductors 3 and 4 incoming to the test distributor TD is relayed or repeated at the test distributor and is imposed in turn on the operating conductors 86 and 81 extending to the test distributor in the distant No. 3 office. As a result the line relay in the distant test distributor which corresponds to the line relay ID of the test distributor TD is permitted to fall back, while the other line relay, corresponding to the line relay 8, is held energized. The control circuit extending to the test connector is thereby broken and the test connector is released.

In connection with the foregoing explanation of the operation of the test distributor in the distant ofiice, it will be understood that on all levels in which these test distributors have access to. test connectors the shaft springs such as S do not close and consequently the test distributors operate as two-digit switches. Under these conditions relays such as l3 and 9 are never energized. If the test distributor in the distant office should have access on some level to outgoing trunks extending to another office then of course the shaft springs of the test distributor in the No. 3 office are adjusted so that on this particular level they will close. It follows that the control conditions relayed from the test distributor TD in the No 2 oflice would be relayed a second time through the test distributor in the No. 3 oflice in the event that such latter test distributor had been operated to select a trunk to another office.

The invention having been described that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

What is claimed is:

1. In combination, a test distributor, a local test trunk and an inter-ofiice test trunk accessible to said distributor, a test trunk incoming to said distributor, means for controlling said distributor over said incoming trunk to connect with either said local or inter-ofiice trunk, means for bridging two conductors of the connected trunk in either case, means responsive to a control condition imposed on the incoming trunk for opening the bridge if the connected trunk is the local trunk, and means responsive to the same control condition for connecting one pole of the exchange battery to one of the bridged conductors and for opening the bridge if the connected trunk is an inter-office trunk.

2. In combination, a test distributor, a test trunk, means for operating said distributor to connect with said test trunk, means in the dis-' change battery to one of said conductors or the other pole of battery to the other of said conduo-tors and to open said bridge.

4. In combination, a test distributor, a test trunk incoming to said distributor, two outgoing test trunks accessible to said distributor, means for controlling the distributor over said incom ing trunk to connect with either'of said outgoing trunks, means for imposing a control con- 1c dition on said incoming trunk, and means in said distributor for repeating said control condition in two different ways depending on which of said outgoing trunks has been connected with.

5. In combination, a test distributor, a test trunk incoming to said distributor, two outgoing test trunks accessible to said distributor, means for controlling the distributor over said incoming trunk to connect with either of said outgoing trunks, means for imposing a control condition on said incoming trunk, means in said distributor for exactly reproducing the control condition in the connected outgoing trunk if one of said outgoing trunks has been connected with, and means for converting said control condition into a different control condition in the connected outgoing trunk if the other outgoing trunk has been connected with.

6. In a test distributor, two line relays, means for operating said distributor under control of said relays, a relay cooperating with said iine relays for repeating control conditions, and means actuated responsive to a particular operation of said distributor for rendering said last mentioned relay responsive to the deenergization of either line relay while the other is held energized.

7. In an automatic switch, two line relays, a control relay, and two circuits for said control relay controlled by said line relays, respectiveiy, said control relay being short circuited when both 40 of said circuits are closed and operative over the other crcuit when either circuit is opened.

8. In a telephone system, a test distributor, local test trunks accessible to said distributor and extending to switches of a test train in the same 5 oifice, a group of inter-office test trunks accessible to said distributor and extending to another office, means for operating said distributor responsive to two digits to select one of said local test trunks or for operating the same responsive 50 to a single digit to select the group of inter-ofiice test trunks, and means responsive to the selection of said group for automatically operating the distributor to select an idle trunk of the group.

9. In a telephone system, a test distributor,

local and inter-office test trunks accessible to said distributor, means for operating said distributor responsive to two digits or a single digit depending on whether a local or inter-office trunk is to be connected with, and means eifective when either connection is completed for conditioning said distributor to repeat impulses over the connected trunk.

10. In a telephone system, a test distributor, means in said distributor normally efiective for operating the same responsive to two successive digits, a changeover relay in said distributor for altering the circuits thereof to provide for a.

hunting movement following an operation responsive to a single digit, a relay responsive to the first digit, and means including said relay and shaft springs cooperating therewith if the first digit has a. particular value for operating said changeover reiay.

11. In a telephone system, a test distributor, incoming test trunk, an outgoing test trunk, means for controlling said distributor over said incoming trunk to connect with said outgoing trunk, means in said distributor for bridging two conductors of said outgoing trunk, a polarized relay included in said bridge, and means controlled by said relay for establishing an inductive connection between a conductor of said outgoing test trunk and a conductor of said incoming test trunk so as to pass tone currents applied to the outgoing trunk back-through the distributor to the incoming trunk.

12. In a telephone system, a test distributor, an incoming test trunk, an outgoing test trunk, means for controlling said distributor over said incoming trunk to connect with said outgoing trunk, means in said distributor for bridging two conductors of said outgoing trunk, a polarized relay included in said bridge, a relay for reversing the current flow in two conductors of said in coming trunk, and a circuitfor said reversing relay controlled by said polarized relay.

13. In an automatic switch having a hunting movement, a stepping magnet for operating the switch in its hunting movement, a slow acting control relay, a circuit for energizing said relay and magnet in parallel, means for first closing said circuit through a resistance which is too high to permit operation of said magnet but low enough to permit operation of said relay, and means responsive to the operation of said relay for closing said circuit over a path which excludes said resistance, thereby operating said magnet.

MORRIS E. GRIFFINS. 

